Active structural members for precision control of components, for instance in aerospace, is an increasing vital need. It is particularly valuable to be able to control motion and vibration caused by forces directed in at least three different senses.
This invention relates to controlling the shape and vibration of structural components in applications, for instance, in spacecraft. Other uses of such structures, which may be termed "intelligent structures," would be in robotics where precise diminutive control is necessary. More particularly, the invention relates to piezoelectric elements which are actuators and sensors embedded or attached to structures particularly fabricated from composites. As such, the movement of these structures can be actively and remotely controlled to a very precise degree.
Composite structures can have embedded piezoelectric actuators and sensors. Strain forces between the embedded piezoelectric elements and the foundation member forming the structure can be transmitted relatively between the elements and the member.
The actuators and sensors can work cooperatively whereby forces from a sensor can cause an actuator to develop counteractive forces. In this manner, when the piezoelectric element constitutes an actuator, selected forces can be transmitted to the foundation member to effect movement of the foundation member. Alternatively, when the foundation member moves, forces from the foundation member can be selectively transmitted to a piezoelectric element which constitutes a sensor. Electronic controls between actuators and sensors can finely monitor and control the movement and shape of the foundation member operative with such piezoelectric elements. An example of such actuator and sensor operation with a foundation member is U.S. Pat. No. 5,022,272 of Bronowicki et al., the contents of which are incorporated by reference herein.
Composite structures are light in weight and are not able to easily dissipate mechanical energy in the form of vibration. As they are also relatively stiff, they are particularly useful in aerospace applications. Using piezoelectric elements embedded with the composite structure is an effective way for actuating and damping movements of the structure. Damping can be applied to compensate for vibrational or other loading forces on the structures.
When piezoelectric elements are bound into a composite structure, movement between the foundation member and the piezoelectric elements in the longitudinal and transverse direction are transmitted between the foundation member and the piezoelectric elements. In this manner, the axial extension or compression of the foundation member can be controlled in the longitudinal direction and the bending of the foundation member can be controlled in a transverse direction.
This degree of control is, however, relatively limited since it is only in the two motive senses, namely axial and bending. In many cases, the foundation member needs control in a third sense of movement, namely torsion. The ability to have an activated structure with a foundation member responsive additionally to torsional forces is not possible with known systems. This drawback is significant.
In aerospace applications, it is not possible to sense or actuate a torsional stress imported to an elongated arm or boom that supports, for example, a remote solar array panel from a main space body. Other applications also require precise control of movement of components, for instance in microtechnology generally, namely in micromechanical applications.
There is an overall vital need to dampen the vibrational movement of a foundation member when it experiences axial, bending and torsional stresses simultaneously. There is thus a need to provide an activated or intelligent structure with the ability to control movement to a degree superior to that of known structures.